1. Field of the Invention
The present invention generally relates to a device array plate, a display panel and a method of preventing electrostatic discharge. More particularly, the present invention relates to a thin film transistor array plate, a liquid crystal display panel and a method of preventing electrostatic discharge.
2. Description of Related Art
Through the rapid development of multi-media technologies, image data are now transmitted mostly in a digital format instead of an analogue format. To fit the life style of modern people, video or image devices have an increasingly light and compact design. Although the conventional display such as cathode ray tube (CRT) has superior display quality and relatively cheap to procure, the electron gun structure within the CRT renders it bulky, heavy and power hungry. Moreover, radiation harmful to the eyes may also be produced. With big leaps in the techniques of manufacturing opto-electronic and semiconductor devices, flat panel displays such as liquid crystal display (LCD) have been rapidly developed. Because a LCD panel is light and slim, has a low operating voltage and emits no hazardous radiations, it has gradually replaced CRT to become one of the mainstream display products.
A liquid crystal display mainly comprises a liquid crystal display panel and a backlight module. The liquid crystal display module further comprises a color filter plate, a thin film transistor array plate and a liquid crystal layer sandwiched between the two substrates. The backlight module provides a planar light source for illuminating the displayed data on the liquid crystal display panel. In addition, the thin film transistor array plate can be divided into a display region and a peripheral circuit region. A plurality of pixel structures is disposed within the display region. The pixel structures comprise an array of thin film transistors and an array of pixel electrodes corresponding to the transistors. A plurality of gate lines and source lines extending from the display region are disposed within the peripheral circuit region. The gate lines and source lines are connected the thin film transistors within the display region for driving the pixel electrodes and twisting of the liquid crystals above.
The process of fabricating the thin film transistor array plate often includes an electrical test to determine the performance of the pixel structures on the substrate and repair any defective devices (such as thin film transistors or pixel electrodes) or lead lines. Conventionally, either a direct contact or a non-contact testing method is used. In a direct contact testing method, probing pins are permitted to contact the external contact pads of gate lines and source lines directly. Thereafter, testing signals are transmitted from a testing station in sequence to check the electrical performance of each thin film transistor. In the non-contact testing method, a plurality of testing lines are serially connected to odd numbered gate lines, even numbered gate lines, odd numbered source lines and even numbered of source lines. Thereafter, testing signals are transmitted to the input terminal of the testing lines and then an optical module is used as a non-contact signal receiver to assess the electrical performance of the thin film transistors.
Furthermore, external factors such as transportation or changes in the environment may lead to the accumulation of some static electric charges in the liquid crystal display panel. When the accumulation of static charges exceed a definite amount, an electrostatic discharge may occur resulting in some damage in the circuit lines or the thin film transistor on the thin film transistor array plate. To protect the circuits and transistors, an outer short ring is often set up inside the peripheral circuit region of the thin film transistor array plate and serially connected to the gate lines and the source lines through a plurality of switching devices. When an excess of electric charges is accumulated on the circuit lines and transistors, the switching device is turned on to permit an outflow of static charges to the outer short ring and prevent any internal discharge.
However, if the thin film transistor array plate with electrostatic discharge protection capability needs to perform a non-contact testing, the peripheral circuit region of the thin film transistor array plate must accommodate a testing circuit as well as an outer short ring. Consequently, the peripheral circuit region may not have an area large enough to accommodate all the circuit lines or else a very complicated circuit layout has to be deployed in the peripheral circuit region. In other words, the process of fabricating the thin film transistor array plate is hard to simplify and hence overall productivity difficult to increase.